This invention relates generally to liquid transfer valves particularly but not limited to those of the rotary operating type for measuring and dispensing precise microliter volumes of samples whereby a pair of measuring chambers is established in a series coupled relationship which is capable of providing simultaneously a pair of precisely measured liquid volumes and directing each to a pair of different predetermined locations, each along with a respective known volume of diluent.
More particularly, the invention provides internal passage means formed in select facing surfaces of said valve elements for isolating the passageways from the periphery of said valve elements so as to prevent liquid from reaching the circumferential exterior of the valve along said facing surfaces.
The liquid transfer metering and transfer valves such as provided in applicant's prior U.S. Pat. Nos. 4,445,391, 4,507,977 and 4,152,391 each include coaxially arranged disc members having opposite faces frictionally engaged and at least one being rotatable relative to the others.
A problem has been encountered involving the occurance of leakage apparently occasioned by liquids such as blood or diluent passing to the faces of the discs surrounding the junction between the communicating passageways and drying at the periphery of said disc surfaces. In addition to requiring disassembly of the valve assembly for cleaning with greater than normal frequency, the valve operation manifests an erratic relative rotation of the valve disc members.
Thus a need has arisen to provide means for materially reducing the frequency of maintenance by preventing such leakage, if it occurs, from traveling to the periphery of the engaged faces. Further and highly desirable is to provide means whereby the interior faces of the valve disc elements can be cleaned automatically.
The only solutions at hand in an effect to alleviate this problem were to cause the discs to be held together in face to face engagement extraordinarily tight making operation of the rotatable one of said elements extremely difficult, if not impossible. Unusual stress results on the parts which increases wear on the faces and causes premature life thereof.